The invention relates generally to aircraft engine mounting systems, and more specifically, it relates to a force balancing actuator to mount a pressure vessel, containing an engine, to aircraft structure.
Recent developments in Advanced Surveillance aircraft require more electrical power than is available from the standard transport aircraft systems. Upgrading a standard transport aircraft for advanced surveillance can require installation of additional or supplementary power for electrical generation. Supplemental power is provided by an air breathing engine installed inside the cabin of the aircraft with inlet and exhaust air plumbed to the outside of the aircraft. The engine is installed inside a pressure vessel that maintains the exterior ambient pressure consistent with the inlet and exhaust. Installing supplemental power inside the cabin without adding excessive weight, excessive volume or transmitting excessive noise and vibration to the crew cabin is the objective.
Patented art of interest includes the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,717,094 issued to Wan T. Chee;
U.S. Pat. No. 4,044,973 issued to Moorehead;
U.S. Pat. No. 3,190,591, granted Jun. 22, 1965, to E. J. Bligard et al.
U.S. Pat. No. 2,724,948, granted Nov. 29, 1955, to G. H. Hiscock et al.
U.S. Pat. No. 2,718,756, granted Sep. 27, 1955, to C. J. McDowall.
The Chee patent describes an Aircraft engine mount system with vibration isolators for mounting jet engines on aircraft and for dampening engine vibrations and, more particularly, to an apparatus that includes elastomeric elements for independently dampening vertical and lateral vibrations which elements are located in a relatively cool strut area to protect them from the heat of the turbine section of the engine.
U.S. Pat. No. 3,190,591, granted Jun. 22, 1965, to E. J. Bligard et al., discloses a core assembly for a forward mount structure for an aircraft engine. U.S. Pat. No. 4,044,973, granted Aug. 30, 1977, to J. R. Moorehead, discloses a forward aircraft engine mount structure having elastomeric mounting pads located close to the engine fan casing. U.S. Pat. Nos. 2,395,143, granted Feb. 19, 1946, to R. H. Prewitt; and 3,288,404, granted Nov. 29, 1966, to W. E. Schmidt et al., disclose cushion mounts for helicopter engines. Schmidt et al. state that, in their system, equal spring rates in all directions perpendicular to the longitudinal axis of the engine are required. U.S. Pat. No. 2,028,549, granted Jan. 21, 1936, to H. C. Lord, discloses a cushioned mount for an automobile engine.
British Patent Specification No. 606,444, dated Aug. 13, 1948, in the name of Lord Manufacturing Company, discloses an aft ring mount for a propeller driven aircraft. A plurality of pins are spaced around the ring and are oriented parallel to the engine axis. Each pin has an elastomeric sleeve and two rubber washers positioned at the axial ends of the sleeves. The sleeves carry torque and longitudinal loads in shear and lateral and vertical loads in compression. The washers act as snubbers to prevent excessive movement in the longitudinal direction.
U.S. Pat. No. 2,724,948, granted Nov. 29, 1955, to G. H. Hiscock et al., discloses a mount system for a gas turbine aircraft engine in which four mounting units are spaced around the engine. The units are positioned inside the engine nacelle between the engine compressor and the nacelle firewall. Each of the four units includes a cushion of alternating disks of metal and resilient material. A casing surrounds each cushion and cooling air is conveyed through the casing to provide a heat barrier between the cushion and the hot region of the engine casing in which the mounting unit is located.
U.S. Pat. No. 3,168,270, granted Feb. 2, 1965, to E. J. Bligard et al., discloses an aft mount for a turbojet engine. The mount includes pivot means for allowing the engine to pivot about a laterally-extending axis to accommodate thermal expansion of the engine. Elastometric elements are positioned around a rigid core in a housing positioned below the pivot axis. The elastomeric elements carry torque and longitudinal loads in shear and vertical and lateral loads in tension and compression. Apparently, the elements above and below the core are independent of the elements at the sides of the core. Bligard et al. state that the stiffness characteristics about three axes were tested at a temperature of 125 [deg] F.
U.S. Pat. No. 2,718,756, granted Sep. 27, 1955, to C. J. McDowall, discloses a rear mount for a propeller gas turbine engine. The engine and engine mount are pivotable relative to the aircraft about a laterally extending pivot axis defined by a connecting bolt. An elastomeric sleeve surrounds the bolt and is positioned between the bolt and the engine mount. No other cushioning elements for the rear mount are disclosed.
The above patent and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.
Standard design practice is to provide flexible features in the inlet and exhaust ducts to avoid excess constraint loads between the airframe and the ducts when the airplane flexes under flight loads. A consequence of flexible features on the inlet and exhaust is an imbalance of pressure forces on the pressure vessel. The area of the inlet and exhaust ducts react exterior pressure the rest of the vessel react the higher cabin pressure. This force imbalance is significant and can be several times greater than the weight of the engine, even when using vibration isolators.